In wireless communications, to improve data transmission efficiency, a proximity service (ProSe) technology is used to enable user equipment (UE) outside coverage of a cell to communicate with a base station by using UE within coverage of the cell, thereby improving data transmission efficiency.
For ease of description, the UE outside coverage of the cell is referred to as remote UE (English: remote UE), and the UE within coverage of the cell is referred to as relay UE (English: relay UE). In the prior art, the remote UE determines the relay UE by using a discovery process in the ProSe technology, and establishes a connection and communication with the relay UE. The relay UE establishes a packet data network (PDN) connection corresponding to a serving/packet data network-gateway (S/P-GW), for transmitting data of the remote UE. The relay UE sends a request message to a mobility management entity (MME), where the request message indicates an access of the remote UE. The MME sends the request message to the S-GW. The S-GW forwards the request message to the P-GW. The P-GW allocates an Internet Protocol (IP) address and a corresponding uplink traffic flow template (TFT) to the remote UE. The P-GW sends the foregoing IP address and the uplink TFT to the relay UE by using the S-GW, the MME, and the base station in sequence. The relay UE sends the foregoing IP address to the remote UE. The remote UE may send the data to the relay UE by using the foregoing IP address, and the relay UE forwards the data to the base station by using the uplink TFT corresponding to the remote UE.
However, when the remote UE leaves coverage of the cell, and accesses a network (for example, the P-GW) by using the relay UE, a situation in which data sending and receiving stop may occur. Consequently, continuity of data transmission cannot be ensured.